1. Field of the Invention
The present invention relates to a sheet finisher, sheet processing apparatus and image forming system that perform Z-folding, stapling or the like to a sheet on which an image is recorded by an image forming apparatus, such as electrophotographic copying machine, printer, facsimile machine, complex machine having these functions, or the like, and to methods for the same.
2. Description of Related Art
Recently, finishers which enable filing sheets by performing punching holes, two-folding, Z-folding to image recording sheets on which images are formed by image forming apparatuses, such as copying machine, printer, complex machine of these, and the like, have been provided.
In earlier technology, as sheet containing apparatuses for containing sheets ejected out from image forming apparatuses in a tray and stapling the sheets, the ones disclosed in the Japanese Patent Laid-Open Publications Nos. 59-43765, 60-183461, and 60-248563, respectively, have been known.
Further, as apparatuses for Z-folding sheets, the ones disclosed in the Japanese Utility-model Laid-Open Publication No. 62-68973, the Japanese Patent Laid-Open Publication No. 4-64577 and the like have been known.
As a sheet finisher for carrying out stapling after Z-folding sheets ejected out from an image forming apparatus, the one is disclosed in the Japanese Patent Laid-Open Publication No. 2001-261220.
In the sheet finishers for performing Z-folding and stapling in the earlier technology, there are some problems as follows.
In the sheet finishers in the earlier technology, the sheets ejected out from an image forming apparatus are stacked and adjusted on a sheet placing table, and then stapled. Thereafter, the sheets are ejected out from the sheet finishers. Then, in order to adjust the sheets sent on the sheet placing table, for example, in the Japanese Patent Laid-Open Publication No. 59-43765, a method such that an impeller-like paddle wheel is rotated in one direction is adopted.
However, in this method, the sheets fed onto the sheet placing table from conveyance rollers reach the paddle wheel by sliding down along the sheet placing table arranged to be inclined in a free state. Therefore, skew is easily caused, so that there is a problem that a certain adjustment cannot be performed.
Particularly, in a sheet finisher for stacking and adjusting the sheets ejected out from an image forming apparatus on a sheet placing table after Z-folding, and then carrying out stapling, the overlapped portion of a Z-folded sheet is swollen, and when a plurality of Z-folded sheets are stacked, the swell of the sheets increases, and the inclined sheets are curved, bent or the like by bowing. Therefore, there occurs a problem that a certain adjustment cannot be performed. The cause of the bowing of the sheets is more remarkable as the inclination of the sheet placing table is made steep.
Further, if there is swell in the sheet overlapped portion in a stack of stapled sheets stacked on the sheet placing table, the front end portion of the stack of sheets in the ejection direction comes apart when the Z-folded sheets are ejected by being conveyed along the sheet placing table after being stapled and by being nipped by sheet ejection rollers. Thereby, the stack of sheets is difficult to be nipped by the rotating sheet ejection rollers, so that bad ejection of sheets is caused.
FIG. 18 is a cross sectional view showing an ejecting state of a stack of Z-folded sheets Sa in a sheet finisher in earlier technology.
The rear end portion of the stack of Z-folded and stapled sheets Sa in the ejection direction is supported by an ejection claw 131A fixed to a turning ejection belt 131 in an accumulation section 130, and conveyed along a sheet placing table 120 arranged to be inclined. The front end portion of the stack of sheets Sa in the ejection direction reaches the nipping position between a driven roller 111 and a driving roller 112 in a sheet ejection section 110. Since the driven roller 111 and the driving roller 112 are waiting in a closed state, the front end portion of the stack of sheets Sa hits the construction member of the sheet ejection section 110, so that the rear end portion of the stack of sheets Sa is pushed upward by the ejection claw 131A which is moving forward. Therefore, buckling occurs in the vicinity of the rear end portion of the stack of sheets Sa, and moreover, tears of sheet occur in the vicinity of a portion stapled by a stapling member 140, which is in the vicinity of the rear end portion of the stack of sheets Sa, when the ejection claw 131A moves along the ejection belt 131 so as to move away from the sheet placing table 120.
Further, FIG. 19 is a cross sectional view showing an ejecting state of a stack of Z-folded sheets Sa in another sheet finisher in the earlier technology.
The rear end portion of the stack of Z-folded and stapled sheets Sa in the ejection direction is supported by an ejection claw 231A fixed to a turning ejection belt 231 in an accumulation section 230, and conveyed along a sheet placing table 220 arranged to be inclined. The front end portion of the conveyed stack of sheets Sa passes through a sheet ejection opening such that a driving roller 212 and a driven roller 211 in a sheet ejection section 210 are separated from each other so as to be in an open state. After the front end portion of the stack of sheets Sa passes through the sheet ejection opening, the driven roller 211 comes down toward the driving roller 212 side, and press-contacts the upper surface of the stack of sheets Sa. Then, the stack of sheets Sa is nipped by the rotating driving roller 212 and the driven roller 211 driven to be rotated via the stack of sheets Sa, and then ejected.
When ejecting the stack of sheets Sa by press-contacting and nipping the front end of the Z-folded portion of the stack of sheets Sa, sag is generated, and at the time of ejecting the stack of sheets Sa, slip occurs between the driven roller 211 and the upper surface of the stack of sheets Sa, so that sag is generated in the vicinity of the front end portion of the Z-folded portion of the stack of sheets Sa. This sag increases during the ejection of the stack of sheets Sa, and therefore, wrinkles are generated in the vicinity of two staples SP in the vicinity of the rear end portion of the stack of sheets Sa, which are stapled by a stapling member 240.